1. Field of the Invention
The present invention relates to ceramic igniter devices, and more particularly, to such devices that regions of differential electrical resistance, particularly in sequence a first conductive zone of relatively low resistance, a power enhancement zone of intermediate resistance, and a further hot or ignition zone of high resistance.
2. Background
Ceramic materials have enjoyed great success as igniters in e.g. gas-fired furnaces, stoves and clothes dryers. Ceramic igniter production includes constructing an electrical circuit through a ceramic component a portion of which is highly resistive and rises in temperature when electrified by a wire lead. See, for instance, U.S. Pat. Nos. 6,028,292; 5,801,361; 5,405,237; and 5,191,508.
Typical igniters have been generally rectangular-shaped elements with a highly resistive “hot zone” at the igniter tip with one or more conductive “cold zones” providing to the hot zone from the opposing igniter end. One currently available igniter, the Mini-Igniter™, available from Norton Igniter Products of Milford, N.H., is designed for 12 volt through 120 volt applications and has a composition comprising aluminum nitride (“AlN”), molybdenum disilicide (“MoSi2”), and silicon carbide (“SiC”).
A variety of performance properties are required of ceramic igniter systems, including high speed or fast time-to-temperature (i.e. time to heat from room temperature to design temperature for ignition) and sufficient robustness to operate for extended periods without replacement. Many conventional igniters, however, do not consistently meet such requirements.
Spark ignition systems are an alternative approach to ceramic igniters. See, for instance, U.S. Pat. No. 5,911,572, for a particular spark igniter said to be useful for ignition of a gas cooking burner. One favorable performance property generally exhibited by a spark ignition is rapid ignition. That is, upon activation, a spark igniter can very rapidly ignite gas or other fuel source.
In certain applications, rapid ignition can be critical. For instance, so-called “instantaneous” water heaters are gaining increased popularity. See, generally, U.S. Pat. Nos. 6,167,845; 5,322,216; and 5,438,642. Rather than storing a fixed volume of heated water, these systems will heat water essentially immediately upon opening of a water line, e.g. a user turning a faucet to the open position. Thus, essentially immediate heating is required upon opening of the water to deliver heated water substantially simultaneously with the water being turned “on”. Such instantaneous water heating systems have generally utilized spark igniters. Current ceramic igniters have provided too slow time-to-temperature performance for commercial use in extremely rapid ignition applications such as required with instantaneous water heaters.
Optimally, ceramic igniters will be effective over a range of voltages. Standard ceramic igniter approval tests require operation at a range of from 85 percent to 110 percent of specified nominal voltages. Those approval tests reflect that the nominal voltage (e.g. 120 volts) delivered to a user will often vary over such a range, even through the course of a single day.
Many prior igniters have had difficulty satisfactorily performing over such an 85-110 percent range. In particular, prior igniters have had difficulty providing sufficiently fast time-to-temperature at the low end of the range (i.e. a line voltage of 85 percent of a specified nominal voltage), and have failed to provide reliable, prolonged performance at high end of the range, i.e. the igniters have prematurely degraded at high line voltages (i.e. 110 percent of a nominal voltage).
Thus, for instance, certain prior ceramic igniters systems have utilized complex electronic control apparatus in conjunction with the igniter. The control apparatus restricts the actual voltage delivered to the igniter to values to within a very narrow range of the specified nominal voltage. Such control apparatus clearly adds complexity and expense to an ignition system.
It thus would be desirable to have new ignition systems. It would be particularly desirable to have ceramic igniters that exhibited performance properties to enable use in new applications. It would be especially desirable to have new ceramic igniters with sufficiently fast time-to-temperature properties to enable use in rapid ignition applications, such as ignition source for instantaneous water heater systems.